OK Piob, from what I gather you're resting your elbows on the table and the gun is not resting on a bag or anything that could be called benching it. Those groups of yours are very good. I would not expect to see 1.5 inch groups at 100 yds. from a beginner and you're doing it with a basic scoped 22 rifle and ammo. I personally think you're what's called a natural shooter.
What would a good shooter be able to do? As Caustic pointed out that's a loaded question. You could have hit the magic combination with that gun of yours and 1.5 inches is the best you'll see. Then again maybe not. You'll have to play with it and see. Shooting tight groups consistently is only part of a much bigger picture. A good shooter in my mind is one who can hit their intended target using various holds, over varying ranges and angles, while being able to take into account things like wind, weather, mirage, varying light conditions and so on.